Retailers rang up solid sales gains in May that topped views as warm weather and tempting promotions put shoppers in more of a buying mood after taking a post-Easter breather. Sales at stores open at least a year rose 4% vs. a year ago, says Ken Perkins, president of Retail Metrics. Analysts forecast a 3.7% rise. The results exclude drugstore giants Walgreen (WAG) and Rite Aid (RAD), which are slated to report May sales next week. Their reports